This invention relates to hydraulic anchor packers for use in well bores and, more particularly, to inflatable anchor packers.
It is well known in the gas and oil drilling industry that hydraulic anchor packers may be used to isolate sections of a well bore and support materials and equipment within a well bore. Conventional hydraulic anchor packers typically comprise a plurality of metallic gripping elements having a serrated surface for engaging the wall of a well bore. The gripping elements are generally mounted on, or operated by, hydraulic pistons which move the gripping elements between gripping and non-gripping positions in response to a hydraulic pressure differential. Although such anchor packers operate very effectively, they are expensive to manufacture and use. They are also unsuitable for use in uncased well bores.
An improved anchor packer is described in UK patent application number 9702148.9. The improved anchor packer incorporates an inflatable packer element which may be inflated with well bore fluid so as to expand an elastomer sleeve into gripping engagement with a well bore wall. This arrangement operates effectively in many situations, however where the downhole end of the packer is located in close proximity to the end of, or a blockage (e.g. a cement plug) in, the well bore, the packer is prone to failure. More specifically, there is a tendency for the elastomer sleeve to rupture due to an increase in static pressure within the well bore annulus. Generally speaking, it is the centre region of the elastomer sleeve located equidistant between the sleeve end portions which first abuts the well bore wall. Once this centre region of the sleeve is in abutment with a well bore, further inflation of the packer element radially expands those portions of the elastomer sleeve located both uphole and downhole of the centre region. However, where the downhole end of-the packer is adjacent, for example, a cement plug, displacement of annulus fluid from between the well bore wall and the downhole half of the elastomer sleeve is restricted. As a result, the uphole half of the elastomer sleeve tends to over inflate and become susceptible to rupturing. This problem is accentuated where expansion ratios of greater than 1:1 are required (e.g. where a 7xc2xdxe2x80x3 OD packer is to be set in a 8xc2xdxe2x80x3 ID well bore, or thereabouts) and a large volume of well bore fluid must be displaced.
In order to overcome this problem, it is known to provide the elastomer sleeve with a floating downhole end portion. During inflation, the cylinder of the packer element upon which the elastomer sleeve is mounted is sucked down relative to the well bore and the floating end portion, and thereby reduces the volume of fluid required to inflate the element and prevents an undesirable increase in static pressure below the packer. This may be detected at the surface by an apparent increase in conveying string weight which occurs because the elastomer sleeve, once abutting the well bore wall, cannot move uphole or downhole. However, a potential problem with the floating end portion system is that the required additional moving parts increase manufacturing costs, require maintenance and can themselves be prone to failure.
It is an object of the present invention to provide an inflatable anchor packer which is inexpensive to manufacture and reliable in use.
It is also an object of the present invention to provide an inflatable anchor packer which may be reliably used adjacent the end of, or a blockage in, a well bore.
The present invention provides a hydraulic anchor packer for use in a well bore comprising; an inflatable packer element incorporating a cylinder and an elastomer sleeve provided on the exterior surface thereof, the elastomer sleeve being retained by retaining means adjacent the cylinder at the end portions of the sleeve but free of the cylinder intermediate the end portions; an aperture defined by the wall of the cylinder for connecting the exterior of the cylinder in a region where the elastomer sleeve is free thereof to the interior of the cylinder; means for causing fluid from within the cylinder to flow through the aperture and between the elastomer sleeve and exterior surface of the cylinder to radially expand the elastomer sleeve; and means for trapping fluid located between the elastomer sleeve and the cylinder to prevent relaxation of the elastomer sleeve; wherein pressure relief means is provided for permitting fluid located exteriorly of the packer to move past the elastomer sleeve as the sleeve expands whilst in engagement with a well bore wall during use.
Thus, as the elastomer sleeve of the present invention radially expands whilst abutting a well bore wall, an increase in fluid pressure below the packer is relieved by the pressure relief means which allows fluid below the packer to be displaced uphole to a location above the packer. The elastomer sleeve is thereby able to inflate freely without the need for one or more floating end portions.
Further features of the present invention are set out in subsidiary claims 2 to 19.